class Foo {
int a = 1
int b = a
}

java.lang.NullPointerException: Cannot invoke method has() on null object
 at org.codehaus.groovy.runtime.NullObject.invokeMethod(NullObject.java:91)
 at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.call(PogoMetaClassSite.java:48)
 at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
 at org.codehaus.groovy.runtime.callsite.NullCallSite.call(NullCallSite.java:35)
 at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
 at org.codehaus.groovy.runtime.callsite.PojoMetaClassSite.call(PojoMetaClassSite.java:52)
 at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:125)
 at org.kohsuke.groovy.sandbox.ScopeTrackingClassCodeExpressionTransformer.isLocalVariable(ScopeTrackingClassCodeExpressionTransformer.groovy:35)
 at org.kohsuke.groovy.sandbox.ScopeTrackingClassCodeExpressionTransformer$isLocalVariable$0.callCurrent(Unknown Source)
 at org.kohsuke.groovy.sandbox.SandboxTransformer$VisitorImpl.innerTransform(SandboxTransformer.groovy:288)
 at org.kohsuke.groovy.sandbox.SandboxTransformer$VisitorImpl.this$6$innerTransform(SandboxTransformer.groovy)
 at sun.reflect.GeneratedMethodAccessor576.invoke(Unknown Source)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
 at java.lang.reflect.Method.invoke(Method.java:498)
 at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
 at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
 at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1213)
 at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1022)
 at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.callCurrent(PogoMetaClassSite.java:69)
 at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:166)
 at org.kohsuke.groovy.sandbox.SandboxTransformer$VisitorImpl.transform(SandboxTransformer.groovy:188)
 at org.codehaus.groovy.ast.ClassCodeExpressionTransformer.visitField(ClassCodeExpressionTransformer.java:68)
 at com.cloudbees.groovy.cps.SandboxCpsTransformer.visitNontransformedField(SandboxCpsTransformer.java:46)
 at com.cloudbees.groovy.cps.CpsTransformer.call(CpsTransformer.java:132)
 at com.cloudbees.groovy.cps.SandboxCpsTransformer.call(SandboxCpsTransformer.java:26)
 at org.codehaus.groovy.control.CompilationUnit.applyToPrimaryClassNodes(CompilationUnit.java:1065)
Caused: BUG! exception in phase 'canonicalization' in source unit 'WorkflowScript' unexpected NullpointerException
 at org.codehaus.groovy.control.CompilationUnit.applyToPrimaryClassNodes(CompilationUnit.java:1070)
 at org.codehaus.groovy.control.CompilationUnit.doPhaseOperation(CompilationUnit.java:603)
 at org.codehaus.groovy.control.CompilationUnit.processPhaseOperations(CompilationUnit.java:581)